Genetic variability and heritability of some selected of cowpea (Vigna unguiculata (L) Walp) lines

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1 Genetic variability and heritability of some selected of cowpea (Vigna unguiculata (L) Walp) lines A.H. Inuwa, H.A. Ajeigbe *, S.G. Muhammed and Y. Mustapha Department of Plant Science, Bayero University, KanoNigeria International Crops Research Institute for the Semi Arid Tropics, KanoNigeria Department of Agronomy, Bayero University, KanoNigeria Corresponding Abstract The success of most crop improvement programs largely depends upon the genetic variability and the heritability of desirable traits. The magnitude and type of genetic variability help the breeder to determine the selection criteria and breeding schemes to be used for improvement purposes. Two different but related experiments, one in 0 rainy season (August to November) and the second in 0 dry season (February to May) were carried out at ICRISAT Kano, Nigeria screen house to estimate the genetic variability and heritability of some traits in selected cowpea lines. Results of the study showed that there were considerable variations among the lines for duration of vegetative and reproductive phase and for yield characters (seed/pod, number of pod/plant, weight of pod/plant, and 00 seed weight). Broad sense heritability estimate (h ) was 8% for 00 seed weight, % for Number of seed per pod, 8% for days to first flower and 6% for number of root nodules. This information showed that there is sufficient genetic variability to justify selection for improvement in the cowpea. This result will be of immense practical uses for plant breeders to choose parent of interest to meet different breeding objectives. Introduction Cowpea (Vigna unguiculata (L) Walp) is the most important food legume in the dry savannas of West Africa where it is an important source of vegetable protein in the daily diets of the rural and urban masses as well as nutritious fodder for ruminant livestock in (Ajeigbe et al., 008). However, due to a number of biotic and abiotic constraints, the grain and fodder yields of cowpea are low in the varying cropping systems of subsistence farmers in the dry savannas of West Africa. The International Institute of Tropical Agriculture (IITA) and several National Research Institutes in West Africa are therefore continuously developing improved lines of cowpea to alleviate these constraints. The development of superior crop lines depends mainly on the genetic diversity available for the crop (Baudoin and Marechal 98). Diversity within wild as well as cultivated forms of cowpea is high and therefore cowpea offers itself for genetic manipulation and breeding. Lines can be prostrate, semi erect, erect or climbing and pods are coiled, round, crescent or linear (Ng and Marechal 98). Development of cultivars with early maturity, acceptable grain quality, resistance to some important diseases and pest has significantly increased the yield and cultivated area of cowpea (Ehlers and Hall, 996). Grain yield is a complex trait; it is influenced by many other important yield contributing characters controlled by polygenes and environmental factors. Any breeding program aiming at increasing yields consider association between yield and its attributes through estimation of genotypic and phenotypic correlation, which help a great deal in formulating selection indices to aid in crop improvement programs. An understanding of the variability existing in a crop is necessary to formulate and accelerate breeding program (Johnson et al, 9). The overall effect of plant breeding on genetic diversity has been a long standing concern in the evolutionary biology of crops plants. Heritability measures the fraction of phenotypic variability that can be attributed to genetic variation. It is an important concept in quantitative genetics, particularly in selective breeding. A study was undertaken to evaluate the genetic variability and heritability of different characters in selected improved cowpea lines available in IITA. The ability to fix atmospheric nitrogen makes legumes excellent components within the various farming systems because they provide residual nitrogen and reduce the needs for mineral nitrogen fertilizers by associated nonlegumes. Intensification of lowinput agricultural production has led to a rapid increase in soil degradation and nutrient depletion in many parts of subsaharan Africa, constituting serious threats to food production and food security Materials and Methods Two different but related trials were conducted in two different seasons: 0 rainy (AugustNovember) and 0 dry season (FebruaryMay) in a screen house of International Crop Research Institute for the SemiArid Tropics (ICRISAT) Kano, Nigeria. The location is on latitude o 8, 8 N and longitude 8 o, 99 E in the Sudan savanna zone of Nigeria. Forty seven (7) lines were used for the rainy season trial while ninety four (9)

2 lines including all the 7 lines were used in the dry season trial. Cowpeas were planted in pot (0 6 cm) arranged in Completely Randomize Design (CRD) with three () replications. The pots were filled with top soil, mixed with manure in the ratio of 0:, and fill to cm to the tip. Pots were arranged on the screen house table and labeled before planting. Six (6) seeds were planted in each pot, and thinned to plants per pot at weeks after planting. Destructive samplings were conducted at 0 days after planting by cutting to plants per pot leaving the remaining plants\pot until maturity. The mean data of rainfall, sunshine, minimum and maximum temperature for the experimental period were collected from Institute of Agricultural Research (IAR) Kano station (Table). The following data were recorded on plants\pot: days to first seed germination, plant height at flowering (cm), number of leaves at flowering, plant biomass at 0 days after planting (g), number of branches at podding, days to 0% flowering, days to 90% maturity, number of pods per pot, number of seed per pod, number of root nodules, weight of pod (g), weight of biomass (g) and 00 seed weight (g). Table. Mean monthly minimum and maximum temperature, sunshine and rainfall from August 0 to May 0. Month Minimum Temp ( o c) Maximum Temp ( o c) Sunshine(h) Rainfall (mm) August September October November December January February March April May Trace STATISTICAL ANALYSIS The data collected were subjected to analysis of (ANOVA) using Genstat discovery statistic software. Estimation of Genetic parameters In order to assess and quantify the genotypic variability among the lines for the characters under study, the following parameters were estimated as given below. Estimation of components Phenotypic and genotypic s were estimated using following formula, MS (variety) MS (error) Genotypic = Number of replications (r) Phenotypic = Genotypic + MS error Heritability (h ): Heritability in broad sense was computed as the ratio of genetic to the total phenotypic as suggested by Hanson et al. (96) and expressed as percentage. Genetic Heritability (h ) = 00 Phenotypic Results The results of the statistical analysis of 0 rainy season data are shown in Table. Significant differences were observed among the cowpea lines for all the variable measured. Large variability was observed for days to 0% flowering, days to 90% maturity and number of root nodules in descending order. The least variation was observed for plant weight at 0 days and pod weight for the rainy season, the genotypic for 00 seed weight were greater than the error s. Wide ranges of difference for genotypic coefficient of variation were observed for the characters studied. Biomass weight and number of pod per pot had lower broad sense heritability (.0 and

3 7.76% respectively) compared to other characters while number of root nodules (.8%) and days to first germination had the highest broad sense heritability. Table. Mean and variability parameters for twelve characters in cowpea genotypes during 0 rainy season S/N Character Grand Mean MS Error Genotypic Phenotypic Heritability (H )% Plant height at flower initiation Plant biomass at 0 days(g) Days to 0% flowering Days to 90% maturity Days to first germination Number of branches at podding Number of leaves at flow Number of Root nodules Number of pods per pot Number of seeds per pod Weight of biomass (g) Weight of pod (g) Results of the analysis of the dry season data are shown in Table. Large variability were also observed for plant weight at 0 days, plant height and leaves petiole length, while least variability were observed for standard petal length and breadth. High heritability was also estimated for 00 seed weight (66.%), number of root nodules (.%) and plant height (7.7%), while weight of pod and weight of biomass showed least heritability of. and 6.0% respectively. In similar trend to the Rainy season, heritability estimated for 00 seed weight and numbers of root nodules were also found to be high. Discussions Generally, large genotypic variation may be caused by small means square relative to large error terms, or vice versa. In this study, proportion of total variation attributable to the error was relatively small. The moderatetolarge genetic and heritability obtained in the present study suggest that substantial residual genetic variability is still available to ensure good progress from further selection for the desired characters, which in turn will lead to increase in grain yield. High heritability estimates (h ) was obtained for 00seed weight, number of root nodules, plant height and days to 0% flowering in the two experiments. This suggests that selection for these characters would be effective for further improvement. The results of the present study corroborate those of Idahosa et al (00); Omoigui et al. (00); Xu et al., (009); and Lesly (00). While Kohli et al (97) and Omoigui et al (00) reported low heritability in weight of biomass and number of pod which was also obtained in the present studies. The low genetic coefficient of variation and heritability obtained for grain yield is not particularly surprising since yield is a product of many complex characters. Therefore, direct selection for grain yield improvement may not be possible, but through indirect selection of other secondary traits may be feasible. However, the low genetic coefficient of variation and heritability obtained for pods per pot and biomass weight per pot are at with those of Ogunbodede and Fatula (98) who reported high broad sense heritability for these traits. Within the range of materials used in this study, there exist substantial genetic coefficient of variation and heritability in the characters studied to warrant selection in the genotypes for further improvement. The level of genetic variability observed for different characters would be useful for breeding lines of cowpea for high yield. The high heritability estimates obtained for days to first flower, number of root nodules, number of seed per pod, and 00seed weight, suggests that these characters are highly heritable and therefore the traits can be easily transferred from parent to offspring. The high to moderate heritability for root nodules can be used where the management of Biological Nitrogen Fixation (BNF) would help improved yields of cowpeas in tropical farming system. Conclusion The present studies have shown that enough variability and genetic heritability exist in the studied characters among cowpea lines in the IITA germplasm for breeders to exploit for further improvement of released cowpea varieties. Major constraints to increased cowpea productivities include diseases, insect pests and parasitic weeds attack. There

4 is therefore the need for genetic researches to be conducted on cowpea for variability and heritability for these constraints. Table. Mean and variability parameters for twenty characters in cowpea genotypes during 0 dry season S/N Character Mean MS Error Genotypic Phenotypic Heritability (H )% Plant height at flower initiation Plant weight at 0 days(g) Days to 0% flowering Days to 90% maturity Days to initial germination Internodes length Leaf stalk length Leaflet Leaves petiole length Leaves petiole breadth Number of branches at pd Number of leaves at flow Number of root nodules Number of pods/pot Number of seeds/pod Standard petal breadth Standard petal length Weight of biomass(g) Weight of pod(g) 00 seed weight(g) REFERENCES Ajeigbe, H.A.,Ihedioha, D., and Chikoye, D. (008). Variations in Physicochemical Properties of Seed of Selected Improved Cowpea Lines. African Journal of Biotechnology Vol. 7 (0), pp. 696, 0 October, 008 Baudoin, J.P. and Marechal, R. (98). Genetic Diversity in Vigna. In: Cowpea Research, Production and Utilization. S.R.Singh and K.O. Rachie (eds.) 98 John Wiley and Sons Ltd. Pp 0 Ehlers, J.D. and Hall, A.E.(996). Genotypic Classification of Cowpea Based on Responses to Heat and Photoperiod. Crop Science.6: Hanson, G.H., Robinson, H.F.and Comstock, R.E. (96).Biometrical Studies of Yield in Segregating Populations of Korean Lependeza. Agronomy Journal, 8: Idahosa, D.O, Alika, J.E, and Omoregie, A.U. (00). Genetic Variability, Heritability and Expected Genetic Advance as Indices for Yield and Yield Components Selection in Cowpea (Vigna unguiculata (L)Walp). Academia arena (). 6 Johnson, H.W., Robinson, H. and Comstock, R.F.(9). Estimates of Genetic and Environmental Variability in Soybean. Agronomy Journal, 7: 8. Kohli. K. S., Singh, C. B., Singh, A., Mehra, K. L., and Magoon, M. L. (97), Variability of quantitative characters in a world collection of cowpea. Interregional comparisms. Genetic Agraria. : Lesly, W. D.(00).Characterization and Evaluation of Cowpea [Vigna unguiculata (L.) Walp.] Germplasm. M.Sc. thesis. University of Agricultural Sciences, Dharwad Ng, N.Q. and Marechal, R. (98). Cowpea Taxonomy, Origin and Germplasm. In: Cowpea Research, Production and Utilization. S.R.Singh and K.O. Rachie (eds.) 98 John Wiley and Sons Ltd. pp Ogunbodede, B.A, and Fatula, T. (98). A Note on the Heritability of Pod Length and Number of Seeds per Pod in Cowpea (Vigna unguculata (L.) (Walp) Traits. East Africa. Agriculture and Forestry Journal. 0: 8900 Omoigui, L.O.,Ishiyaku, M.F.,.Kamara, A.Y.,Alabi, S.O., and Mohammed, S.G. (00). Genetic Variability and Heritability Studies of Some Reproductive Traits in Cowpea (Vigna unguiculata (L) Walp). African Journal of Biotechnology, Vol. / pp 99

5 Xu, N.W.,Xu, S., and Ehlers, J.(009). Estimating the Broad Sense Heritability of Early Growth of Cowpea. International Journal of Plant Genomics. Pp

Effect of Drought on the Yields of Different Cowpea Cultivars and Their Response to Time of Planting in Kano State, Nigeria

Effect of Drought on the Yields of Different Cowpea Cultivars and Their Response to Time of Planting in Kano State, Nigeria Communication International Journal of Environment and Bioenergy, 2013, 6(3): 171-176 International Journal of Environment and Bioenergy Journal homepage: www.modernscientificpress.com/journals/ijee.aspx